1. Field
The present disclosure relates to the field of communications, and in particular to a signal processing apparatus, a signal transmitting apparatus and a receiver.
2. Description of the Related Art
As the development of optical communication technologies, the appearance of coherent receivers and high-speed digital signal processing (DSP) technologies push forward continuous increase of capacities of optical communication systems, conventional binary on-off keying (OOK) modulation formats are continuously upgraded, and quadrature phase shift keying (QPSK), 16QAM (quadrature amplitude modulation) and QAM formats of higher orders appear.
On the other hand, as a flexible optical network can maximize resource configuration of the network, modulation formats capable of supporting resource allocation are favored by people. Currently, more attention is paid to the study of an orthogonal frequency division multiplexing (OFDM) modulation format. Although an OFDM system has a smaller scheduling force relative to a single-carrier system, it has some inherent defects. For example, neighboring channels are subjected to relatively large interference, and further improvement of spectrum utilization ratio is limited, etc. For a frequency division multiplexing (FDM) modulation format of a broader sense, when its spectrum is strictly limited, a problem of spectrum spreading may be avoided, and widths of subcarriers may be flexibly adjusted at the same time. Thus, the FDM technology has a wider application prospect.
In an FDM system, the orders of the modulation formats of the subcarriers are relatively high. In a case where the same bit error rate is reached, a high-order modulation format not only has a relatively high requirement on an optical signal to noise ratio in a link, but also a descending tolerance for a phase noise of a laser. Hence, the phase noise of the laser needs to be compensated, so as to recover a carrier phase. Currently, there is not effective method for compensating for a phase noise of a laser for an FDM system to recover a carrier phase. Furthermore, for an OFDM system, multi-frame signals of received signals need to be obtained in a time domain, and changes of phases of the multi-frame signals need to be analyzed. Therefore, down-sampling and equalization processing need to be performed first on the received signals.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.